Preparation

Preheat oven to 350 degrees. Butter a 9-by-5-inch loaf pan. Grate the zest from 2 blood oranges and place in a large bowl with sugar. Using your fingers, rub ingredients together until orange zest is evenly distributed in sugar (sugar will be an orange color).Supreme an orange: Cut off bottom and top so fruit is exposed and orange can stand upright on a cutting board. Cut away peel and pith, following curve of fruit with your knife. Cut orange segments out of their connective membranes and let them fall into a bowl. Repeat with another orange. Break up segments with your fingers to about 1/4-inch pieces. Halve remaining orange and squeeze juice into a measuring cup; you’ll have about 1/4 cup (One orange yielded ¼ cup for me). Add buttermilk or yogurt to juice until you have 2/3 cup liquid altogether. Pour mixture into bowl with sugar and whisk well. Whisk in eggs and then olive oil.In another bowl, whisk together all-purpose flour, spelt flour, baking powder, baking soda and salt. Using a spatula or wooden spoon, gently stir dry ingredients into wet ones. Fold in pieces of orange segments. Pour batter into prepared pan.Bake cake for 50 to 55 minutes, or until it is golden and a knife inserted into center comes out clean. Cool on a rack for 5 minutes, then unmold and cool to room temperature, right-side up.